1. Field of the Invention
The present invention relates to a developing unit, a process cartridge, and a developing cartridge for developing images using developing agent.
2. Description of Related Art
A conventional image forming device includes a known developing unit that develops electrostatic latent images into visible images using charged particles of toner. This type of developing unit can leak toner. The leaked toner can stain the interior of the image forming device and recording sheets, thereby degrading printing quality. The leaked toner can also stain the user""s hands or clothes during replacement of the developing unit.
One such developing unit with this problem includes a developing roller and a layer thickness regulating blade. The developing roller transports toner on its surface, and the layer thickness regulating blade regulates the toner on the surface of the developing roller to a thin layer. The layer thickness regulating blade includes a stainless steel plate spring and a resin or rubber pressing member, both formed to the same length in their lengthwise direction. Non magnetic single component developing agent is used as toner. The toner easily leaks from around the edges of the developing roller as the developing roller rotates.
Conventionally, various configurations have been provided inside the developing unit in order to prevent toner leakage. As will be described next, side seals and a lower film are examples of configuration provided for preventing toner leakage.
The side seals are formed from a urethane sponge with a Teflon(trademark) felt attached thereto. The urethane sponge needs to be sufficiently soft and have a low compression set. The Teflon(trademark) felt can be pressed with sufficient pressing force against the developing roller, without increasing rotational torque required for rotating the developing roller.
The lower film is usually made from urethane rubber or a polyethylene terephthalate (PET) sheet. Although the urethane rubber provides a sufficiently soft pressing force, it has insufficiently low stiffness on its own, and so needs to be pressed from behind by a sponge or other member. The PET sheet is stiffer than the urethane rubber film and so does not need to be pressed from behind by a sponge member. Therefore, the PET sheet makes assembly processes easier than does the urethane rubber film.
However, the present inventors have discovered that when side seals and a lower film are used in configuration for preventing leaks, toner can easily leak between contacting surfaces of the lower film and the side seal while the side seal rubs against the outer periphery surface of the developing roller. For example, if the lower film is extended toward, but does not overlap with, the side seals, then toner can leak through gaps between the lower film and the side seals. On the other, if the lower film is extended to span across the side seals, so that the ends of the side seal extend beyond the side seals, then a step will develop where the lower film overlaps with each side seal. In this case, when the developing roller is disposed in contact with both of the lower film and the side seal, these steps form small gaps equivalent to the thickness of the lower film. Toner can leak through these gaps.
Polymerized toner has excellent fluidity. Therefore, when polymerized toner is used it can easily leak through even the smallest gaps.
It is conceivable to extend the ends of the lower film to near the center of where the side seals slide against the developing roller. With this conceivable configuration, the step portion between the lower film and the side seal will end at the end of the lower film, that is, near the middle of the side seal. As a result, the gap will be cut off near the middle of the side seal, so even it polymerized toner is used, toner leaks can be almost completely prevented. However, this conceivable configuration also has a leak problem because of the following circumstances.
The side seals must be formed with a thickness that takes into consideration the amount that they are compressed by the developing roller. If the compression amount of the side seals is too small, then the pressing force against the developing roller will be too small to provide a proper seal, so that toner will leak. On the other hand, if the compression force of the side seals is too large, then an excessively large pressing force will develop between the side seals and the developing roller. As a result, a great deal of rotational torque will be required to rotate the developing roller. In order to achieve an optimum pressing force, it is conceivable to form the case with the surfaces where the side seals are attached retracted lower than the surface where the lower seal is attached. The side seals are then adhered into these indented attachment areas.
However, with this conceivable configuration, a step is formed between the indented side seal attachment area and the lower seal attachment area. When the developing roller presses down on the side seals, the side seals slide along the surface of the step portion as they compress. Also, during developing operations the side seals vibrate slightly in association with rotation of the developing roller, so that the side surface of the side seals slightly slides against the surface of the step portion. Because the side seal must be able to slide against the surface of the step portion in these instances, the side surface of the side seal cannot be adhered to the surface of the step portion, for example, by two-sided tape. Also, the interface between the plastic surface of the step portion and the sponge material of the side seals has extremely poor sealing properties, so polymerized toner, which has a extremely high fluidity, can easily leak between such an interface.
Also, the developing roller is not yet installed when ends of the lower film are being attached to the side seals, so the side seals are not yet compressed by the developing roller at this time. Therefore, if the ends of the lower film are extended to near the center of where the side seals slide against the developing roller, then the lower film must be bent upward because of the difference in height between the lower film attachment area and the upper surface of the side seals. Afterward, when the developing roller is attached, the side seals and also both ends of the lower film are compressed by the developing roller. As a result, the lower film can deform or shift out of position from where it is adhered, thereby lowering its sealing capacity.
It is an objective of the present invention to overcome the above-described problems, and to provide a developing unit and a process cartridge capable of reliably preventing toner leaks from connecting portions between a lower film and side seals.
To achieve this objective, a developing device according to a first aspect of the present invention is for developing a latent static-electric image into a visible image from developer, wherein the developing device includes a developing case, a developer bearing body, end leak prevention members, a lower-edge leak prevention member, and attachment-surface-border leak prevention members having the following configuration.
The developing case is for holding developer. The developing case is formed with an opening that extends in a lengthwise direction. The developing case includes a lower-edge attachment surface and two end attachment surfaces at the opening. The end attachment surfaces are on either side of and bordering the lower-edge attachment surface in the lengthwise direction and are indented with respect to the lower-edge attachment surface.
The developer bearing body is disposed in the opening of the developing case in confrontation with the latent static-electric image, with lengthwise ends of the developer bearing body rotatably supported on the developing case.
The end leak prevention members are each attached on a corresponding end attachment surface of the developing case. Each is in sliding contact with a corresponding peripheral surface of the developer bearing body near a corresponding lengthwise end of the developer bearing body.
The lower-edge leak prevention member is attached on the lower-edge attachment surface of the developing case and extends in the lengthwise direction. The lower-edge leak prevention member is in sliding contact along a length of the developer bearing body at a position downstream, with respect to rotational direction of the developer bearing body, from where the developer bearing body confronts the latent static-electric image.
The attachment-surface-border leak prevention members are each made from a resilient foam material. Each is attached to the lower-edge attachment surface at a corresponding border position between the lower-edge attachment surface and a corresponding end attachment surface, with at least a portion of one side surface in contact with a portion of one side surface of a corresponding end leak prevention member.
According to a second aspect of the present invention, a process cartridge adapted for free attachment and detachment with respect to an image forming device, includes a latent static-electric image bearing body formed with a latent static-electric image; and the developing device according to the first aspect of the present invention.
According to a third aspect of the present invention, a developing device includes a developing case, a developer bearing body, a lower-edge leak prevention member, and end leak prevention members with the following configuration.
The developing case is for holding developer. The developing case is formed with an opening that extends in a lengthwise direction. The developing case includes a lower-edge attachment surface.
The developer bearing body is disposed in the opening of the developing case in opposition with the latent static-electric image.
The lower-edge leak prevention member extends in the lengthwise direction of the opening and includes an attached portion and a free end. The attached portion is attached on the lower-edge attachment surface of the developing case. The free end is in sliding contact along a length of the developer bearing body downstream, with respect to rotational direction of the developer bearing body, from where the developer bearing body confronts the latent static-electric image.
The end leak prevention members each include a sliding contact member and a resilient base member. Each sliding contact member is in sliding contact with a corresponding peripheral surface of the developer bearing body near a corresponding lengthwise end of the developer bearing body. Each base member as an upstream end with respect to rotational direction of the developer bearing body. The upstream end of each base member s positioned in an overlapping condition with the lower film 114 between the free end of the lower-edge leak prevention member and where the lower-edge leak prevention member is attached to the lower-edge attachment surface with respect to rotational direction of the developer bearing body.
According to a fourth aspect of the present invention, a process cartridge adapted for free attachment and detachment with respect to an image forming device, includes a latent static-electric image bearing body formed with a latent static-electric image; and the developing device according to the third aspect of the present invention.
According to a fifth aspect of the present invention, a developing device includes a developing case, a developer bearing body, end leak prevention members, a lower-edge leak prevention member, and attachment-surface-border leak prevention members with the following configuration.
The developing case is for holding developer. The developing case is formed with an opening that extends in a lengthwise direction. The developing case is provided with end attachment surfaces and a lower-edge attachment surface. The end attachment surfaces is formed lower than the lower-edge attachment surface.
The developer bearing body is disposed in the opening of the developing case in opposition with the latent static-electric image, with lengthwise ends of the developer bearing body rotatably supported on the developing case.
The end leak prevention members each slidingly contact a corresponding peripheral surface of the developer bearing body near a corresponding lengthwise end of the developer bearing body.
The lower-edge leak prevention member is attached on the lower-edge attachment surface of the developing case and extends in the lengthwise direction. The lower-edge leak prevention member is in sliding contact along a length of the developer bearing body.
The attachment-surface-border leak prevention members formed from a resilient foam material, and is disposed at borders between the lower-edge attachment surface and the end attachment surfaces. The lower-edge leak prevention member exposes the attachment-surface-border leak prevention members between the lower-edge leak prevention member and the end leak prevention members.
According to a sixth aspect of the present invention, a process cartridge adapted for free attachment and detachment with respect to an image forming device, includes a latent static-electric image bearing body formed with a latent static-electric image; and the developing device according to the fifth aspect of the present invention.